Solar Panel Efficiency Question

[Letterkenny]

After some failed Googling, thought I would throw this one here. If I have two different solar panels at both 100w at 18.5v but one is 15% efficient and the other being 21% efficient, what does that mean? Is it that the more efficient panel will produce more electricity on average or that by being more efficient, the panel would be smaller?

[cal40john]

One panel could have more photovoltaic surface, or the way they measured them could be different. A favorite saying of a friend, "The nice thing about standards are that there are so many to choose from." (I searched and found he got it from someone else.)

https://www.vivintsolar.com/learning...e-solar-panels
Most figures say that solar panels are roughly between 15% and 18% efficient, meaning that 15% to 18% of the sunlight they absorb is converted into electricity while the rest hits the solar panel and warms the surface like it would anything else.

[Pete7]

15% isn't great and suggests an older design of panel. Also if you look at the manufacturers specifications you will often see the same size panel has different outputs.

With the two you have now I would just use them if they meet your needs.

Pete

[paul2884]

could be that both panels are capable of producing 100watts but one will need more sun hitting it to do so? at first glance it does seem strange that they are both the same rating but different efficiencies but that is only the maximum they can produce.

[Pete7]

Or even a slight manufacturing defect, but I doubt they test every panel just the odd one in a batch at best.

Pete

[Letterkenny]

Well my original question was posted in theory but here are the two panels that I am referring to. The Ecoflow is 10 watts more but otherwise the two are very close in specification with the exception of the Renogy being under 15% efficient per the specs and the Ecoflow being 21%. Curious what that means in the real word and if I should get rid of the Renogy panels in favor of something more similar to the Ecoflow.

https://ecoflow.com/products/110w-solar-panel
https://www.renogy.com/100-watt-12-v...e-solar-panel/

[Pete7]

Alternatively keep both with separate MPPTs then it doesn't matter what the efficiency is.

Pete

[smac999]

100w is 100w. The more efficient one will be smaller. More efficient per size.

[GordMay]

By their own numbers, the Renogy panels are actually more efficient [13.89W/Sq Ft], than the EcoFlo panels [12.55W/Sq Ft].
Actual % efficiency will vary with assumed solar insolation [Incoming Watts/Area ÷ output Watts/Area ]
So, for comparison purposes:
If I assume an average’ solar insolation [input] of ± 90 Watts per Square Foot of exposed panel, I calcultate efficiencies of:
Eco Flo: 12.55 (input) ÷ 90 (output) = < 14% Calculated Efficiency
Renogy: 13.89 (input) ÷ 90 (output) = >15.4% Calculated Efficiency

EcoFlow 110W Solar Panel
Rated Power 110 Watts
Dimensions: 62.5 x 20.2 x 1.0 in = 1,262.5 Sq. In./8.767 Sq Ft.
CLAIMED Efficiency: 21-22%?
Calculated Output: 110W ÷ 8.767 = 12.55 W/Sq Ft

Renogy 100W Flexible Solar Panel
Rated Power 100 Watts
Dimensions: 48.0 x 21.6 x 0.08 in = 1,036.8 Sq. In./7.2 Sq. Ft.
CLAIMED Efficiency: 14.9%?
Calculated Output: 100W ÷ 7.2 = 13.89 W/Sq Ft

Another metric for comparison, is cost per watt.

[Dave Lochner]

Not all cells are alike, better cells produce more power at lower levels of light. A number of factors contribute to this. In real life what matters is how much you can expect from a solar panel. Nigel Calder suggests that on average a panel will produce 3x times its nominal capacity, i.e., a 100 watt panel will produce 300 watt hours on a good day, better more efficient (more expensive) panels will do better, poorer quality (cheaper) panels less. The linked article is a good review of current panels.

https://www.proboat.com/2019/11/adva...onboard-solar/

[Wayfarer1008]

Being a person that used to maintain remote seismograph stations efficiency is all relative. In general, the more expensive your panel the greater efficiency. Materials and manufacturing methods have a lot to do with this so as they say you get what you pay for.
The problem that is not presented is the fact that the life cycle of solar panels like anything exposed to the elements varies tremendously. Corrosion, Heat cool cycling, and UV oxidation to the solar panel collection surface all add up to limit the life of a panel. With for the remote stations, I was maintaining we would replace the panels generally when the efficiency of the panel dropped under 5%. This would generally happen between 10 to 15 years in the field Irregardless of the efficacy when new.

[Moontide]

The 15% panel will consistenly put out less watts than the 21% given the same conditions, until the real world conditions exceed the lab standard conditions. The theory of standardized rating conditions is to let one compare apples to apples.

My guess is the 15% panel is a good bit older than the 21% as efficiency has been going up over time.

[Letterkenny]

Both panels are new. Per Gords calc, there is some issues on the space as the Ecoflow is a series of smaller rigid panels with gaps to enable it to fold up which adds area without solar capacity. I haven’t used them both at the same time but I was seeing more output from the Ecoflow than the Renogy. Different days and what not so hard to pinpoint much.

[sailormed]

Originally Posted by Pete7

Or even a slight manufacturing defect, but I doubt they test every panel just the odd one in a batch at best.

Pete

As far as I know the manufacturing process they test every panel. They they sell the excellant efficiency in panels under their top brand, the lower under a lower brand and the rest they sell to bulk buyers who sell via on eBay and other channels.

[Adelie]

Originally Posted by cal40john

One panel could have more photovoltaic surface, or the way they measured them could be different. A favorite saying of a friend, "The nice thing about standards are that there are so many to choose from." (I searched and found he got it from someone else.)
…...

Sounds like Norm.